One component of treatment resistance of small cell lung cancer (SCLC) may involve phenotypic transitions of this tumor towards the non-SCLC forms of lung cancer. An in-vitro model for SCLC phenotypic progression has been developed which involves complementation events between inserted c-myc and Ha-ras oncogenes to produce a form of large cell carcinoma. This phenotypic transition is accompanied by the induction of the expression of the epidermal growth factor receptor (EGFR) and its ligand, transforming growth factor-alpha (TGF-alpha). Initial data suggest that a key step in the complementation events between the myc and ras genes may be c-myc induced expression of the beta isoform of protein kinase C. The studies in this proposal examine this hypothesis directly, and seek to determine the molecular mechanisms involved in this phenotypic transition. The first series of experiments is designed to designed to determine whether PKC-beta and/or EGFR expression directly mediate the myc-ras induced conversion of the small cell to the large cell lung cancer phenotype by studying the phenotype resulting from the insertion of PKC-beta and erb-B constructs into the described SCLC cell lines. In other studies, the phenotypes resulting from abrogation of PKC-beta and -alpha isoform expression will be evaluated by transfection of PKC isoform-specific antisense sequences into these SCLC cells. Studies designed to determine whether activation of c- myc gene expression acutely activates PKC-beta gene expression will utilize transfection of an inducible myc construct into these SCLC cell lines.Depending on the outcome of these experiments, the promoter regions of the PKC-beta and -alpha isoform genes will be cloned and used in reporter gene studies in myc-transfected cells. Finally, if the above studies suggest transcriptional activation of the PKC-beta gene by myc, a long-term goal of this proposal will be to determine whether there are specific DNA binding sites for the c-myc or other proteins in the regulatory region of PKC-beta which modulate the observed transcription.